
Live & historical FX, 168 pairs back to 1999, Frankfurter-compatible, free 10k/mo.
Exchangerate.dev API is a free Currency Exchange API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Start with one API call, browse the REST reference, or pull FX history back to 1999 on Plus or Pro in JSON, CSV or Parquet.
Details from exchangerate.dev.

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Real-time foreign exchange rates for major currency pairs
The Exchangerate.dev API is provided by exchangerate.dev (exchangerate.dev). Start with one API call, browse the REST reference, or pull FX history back to 1999 on Plus or Pro in JSON, CSV or Parquet.
Yes. The Exchangerate.dev API is listed in the Currency Exchange category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Exchangerate.dev API requires no authentication, so you can start making requests without signing up.
CORS support for the Exchangerate.dev API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Exchangerate.dev API is served over HTTPS, so it's safe to use in production.